Laser marking is a technique of providing various industrial products with characters, signs, markings, etc. by irradiating laser light.
Due to such advantages as good appearance, almost no possibility of being deteriorated, a short processing time, and labor-saving properties, the laser marking has been adopted in various fields.
Laser marking was generally performed on the surface of a product. Therefore, if the surface is marred or fouled, etc, a good appearance might not be obtained. Moreover, due to the fear of falsification or erasion, there was also a problem that important data could not be drawn.
Under such circumstances, a technique has been proposed to prevent laser marking from being marred or fouled, and further, from falsified or erased, has been proposed.
For example, a technique has been proposed in which, while stacking a protective layer through which laser light can transmit on a resin matrix on which characters or patterns can be formed by irradiation of laser light, the surface of the resin matrix is irradiated with laser light, whereby characters or patterns are formed (for example, see Patent Document 1).
According to this technique, since characters or patterns are protected by the protective layer, these characters and patterns are prevented from being marred or fouled, and further, prevented from being falsified or erased.
Although laser marking is conducted on many industrial products, it is difficult to conduct laser making on a high-molecular processed product (plastics) which transmits laser light.
The reason therefor is that, in such an object to be processed, since only small amount of laser light is absorbed, an interaction of light and a substance (for example, light-and-heat conversion) is hard to occur.
Under such circumstances, a technology has been proposed which enables laser marking also for an object to be processed consisting of a high-molecular processed product which transmits laser light.
For example, a technology has been proposed in which a substance having a large absorption for laser light (light absorption agent) is dispersed in an object to be processed or applied to the surface of an object to be processed (for example, see Patent Document 2).
According to this technology, since absorptivity of laser light is increased by a substance dispersed or applied, laser marking becomes possible. In particular, in the case of a shaped product coated with a thermoplastic resin composition which contains a specific amount of carbon black, laser marking with a clear contrast becomes possible.
Moreover, a technology has been proposed in which a transparent body, the bottom surface of which is in contact with a solution having a high laser light absorptivity, is irradiated with laser light which has been condensed by means of a lens from the upper surface thereof, and the relative position of the lens and the transparent body are changed such that, as a hole formed in the interface of the transparent body which contacts the solution advances into the inside of the transparent body, the focus of laser light matches the deepest part of the hole, thereby etching a transparent body (see Patent Document 3, for example).
According to this technology, since the laser light, which has passed without being absorbed by the transparent body is absorbed by a solution, laser energy is caused to transmit indirectly to the transparent body which is in contact with this solution, whereby the surface of that transparent body can be etched.